Electrical device



1952 J. F. LEVERS ETAL 1 ELECTRICAL DEVICE Filed June 3. 1947 a". F.LEVERS R.\/. PATCHETT ATTORNEYS memea Jan. 15, gas:

James Frederick Levers and Richard Vernon Patchett, Spondon, near Derby, England, assignors to Celanece Corporation of America, a

corporation of Delaware Application 1 3, 1941, Serial no. 752,188

Great Britain Jlllle 8, 1946 3 Claims. (CL 20163) This invention relates to new or improved electrical devices and is more particularly concerned with novel electrical resistances and their manufacture. j g

The novel electrical resistances of the invention comprise a ribbon woven from a warp of electrically insulating yarn and a weft in the form of a plurality of sections of predetermined length, said weft comprising a wire continuous throughout the length of each section. The number of picks of wire in each section of such a ribbon determines the resistance of the section, and, in practice, it is mostconvenient to weave the ribbon so that the sections contain identical numbers of picks and hence are of identical resistance; resistances of various values can then be made simply by severing from a length of such ribbon pieces containing different numbers of section and when, as is preferred, the weft wire is continuous throughout the woven length, the sections in each piece are already joined electrically in series to form a single resistance.

The sections of tape can be separated from each other by replacing the wire during weaving with a few picks of an electrically insulating yarn. A preferred c'nstruction is one in which each section is followed in succession by two picks of such yarn, two picks of the wire used in weavingthe sections, two more picks of the yarn, two more picks of the wire and then a further two picks of the yarn followed by the next section. With such an arrangement, resistance units comprising one or more of the sections can be severed from a length of ribbon by cutting the ribbon along the innermost pair of yarn picks between the two sections to be parted; the two pairs of wire picks adjacent to I the cuts at each end of the resistance unit can then be unravelled and used as connecting leads, the remaining yarn picks at the ends of the unit preventing unravelling of the wire in the resistance. It is desirable that the picks of yarn between-the sections should be of a colour which contrasts strongly with that of the sections. Naturally more than two picks of the yarn and of the wire picks provided for connecting leads may, if desired, be inserted.

Such a ribbon can be made using an ordinary multiple-head ribbon loom modified to allow the 0.001 diameter.

shuttle normally supplying one web to traverse an extra distance in one direction, the adjacent shuttle being brought into a position suitable for weaving. An alternate use of these shuttles each weaving a predetermined number of picks enables the wire weft supply to be replaced at intervals in the woven construction by the yarn of insulating material while maintaining continuity of the weft wire throughout the woven length.

If desired, connecting leads of stouter crosssection and/or different metal, e. g., copper, can be included in the woven structure. Thus, each section of the ribbon may be followed in succession by two picks of insulating yarn, then one pick of copper wire, then two more picks of insulating yarn, then two picks of the resistance wire, then two more picks of insulating yarn, then two more picks each of resistance wire and yarn, then a second pick of copper wire and a further two picks of insulating yarn, followed by the next resistance section. In such a ribbon the resistance wire, including that in the pairs of picks separated from each section by yarn, is continuous throughout the ribbon and likewise the copper wire is continuous and brought out in loops on each side of the ribbon.) when such a ribbon is out along the innermost yarn picks between two sections, two picks of resistance wire are easily unravelled and can be soldered or welded to one end of the copper wire loop cut simultaneously with the main part of the ribbon. At the other end of the resistance unit made, a similar operation results in a. second copper lead firmly held in the end of the'fabric. Intermediate loops of the copper wire are, of course, cut so as to avoid short circuiting the resistance.

The invention is of particular importance in connection with the use of very fine wire of high specific resistance, for example, wire of less than 0.003" diameter and especially wire of about The composition of the wire may be the usual nickel-chromium and coppernickel alloys used for the manufacture of resistance wires. While the warp yarns space the weft wires apart and the ribbon could in fact be used as such, even if the resistance wire were provided with no other form of insulation, it is preferred to employ wire provided with an insulating sheath, for instance a coating of enamel, or, better still, one or more lappings of insulating yarn. The yarn used may be silk or an organic ester of cellulose, such as cellulose acetate, or regenerated cellulose, whether made from viscose or by the saponificatiorr of a cellulose acetate yarn. A particularly satisfactory product is obtained with a wire having two layers of lapping, the first being of cellulose acetate and the second of silk, the lappings being wound on in opposite directions. Where extremely fine resistance wire is used, however, e. g., of less than 0.001" diameter,'it is generally more convenient to use wire having a single lapping, for example, of silk.

The warp with which the ribbon is woven can be of the same or different texture as that with which the wire is lapped. In general, there should be used a warp of less than, for example, 50 denier, and, in order to achieve the necessary fineness, it is generally desirableto use a continuous filament yarn. Especially satisfactory for the purpose is a yarn of artificial continuous filaments that have been stretched to a high degree, e. g., to or times their original length, in the presence of an agent adapted to facilitate stretching. The stretching operation has the and of greatly increasing the tensile strength of the filaments in terms 01 gms. per denier and also of increasing their fineness in accordance with the degree of stretch imparted. Thus, continuous filament yarns of cellulose acetate having a filament denier of 2/5 may be stretched in the presence of moist steam to 5, 10 or more times their original length, and the resulting fine filaments of l/0.2 filament denier or less can be further reduced in weight without a corresponding diminution in their tensile strength by saponifying the substance of the filaments. Stretched and saponified fine filament yarns of this kind may also be used instead of silk as a lapping for the wire. For this purpose, however, it is preferable that, between the operations of stretching the filaments and saponifying them, they should be subjected to a shrinking treatment which, while slightly reducing their tenacity, increases their extensibility and facilitates the lappin Operation.

The yarn used for spacing the separate sections in the ribbon can be of any suitable insulating material, such as cotton, silk, cellulose acetate or regenerated cellulose, and in general should be of heavier denier than the warp yarns. Generally it is advantage to colour the spacing yarn differently from the colour of the lapped resistance wire, as this simplifies cutting the tape accurately at the required spot.

The tape may be woven in any width which is suitable according to the purpose for which the resistances are required, but in general a width of about 1" has been found to have wide application. With such a width, and using 100 picks per inch ofresistance wire of about 0.001" diameter, tapes having a resistance of from 1,500

to 5,000 ohms per inch, according to the wire used,

can be woven without any dimculty. Using heavier wire and/or fewer picks per inch, tape having a lower resistance per inch may be woven,

while, with even finer wires, resistances of more than 5,000 ohms per inch can be made, e. g., with 120 picks per inch of a nickel-chrome wire of 0.0006" diameter, 1" wide tape having a resistance of about 15,000 ohms per inch can be made. constructional details of one such tape are as follows:

Warn-240 ends of denier, 0.4 filament denier 10 turns per inch, stretched and saponified cellulose acetate yarn drawn 4 ends per dent in a 60s reed. 2 ends as one-plain weave. 2 catch threads of 2/30 denier stretched and saponified cellulose acetate yarn each side.

Weft-50 picks per half-inch of 0.001 diameter Brightray nickel-chrome wire covered. with 6'7 wraps per inch of 26 denier silk and wraps per inch of denier 42 filament cellulose acetate lapping yarn.

In weaving, the warp is separated into sections eachcontaining 50 picks of wire by 2 picks of coloured cotton fillowed by 2 picks of the wire, then 2 further picks of cotton, another 2 picks of wire, 2 more picks of cotton, followed by the next section of 50 picks. This tape has a resistance of about 2,500 ohms per half-inch section, and the sections are of the same resistance within very close limits.

The invention provides a simple and speedy method of manufacturing wire resistances of any desired value with a high degree of accuracy. Thus, individual sections cut from a length of the ribbon made up of equal sections may be used as strain gauges. The resistances may also be used for other purposes where high accuracy is of importance, e. g. in electrical measuring instruments, radio, radiolocation and similar purposes. The ribbon may be woven in sections havinga resistance of the particular value required for the purpose to which it is to be put and the sections subsequently separated from each other. Alternatively, ribbons may be woven with suitable standard sections, resistances of the desired value being made up by dividing the ribbon into lengths containing the required number of sections. Again, a selection of ribbons may be woven with sections having different resistances, e. g.. one ribbon with sections of 10,000 ohms and another with sections of 1,000 ohms, and complete resistances made up with sections taken from any of the ribbons. In making up the resistances it must, however, be borne in mind that allowances must be made for the resistance of the picks provided between each pair of sections for use as resistance leads.

The ribbon may, if desired, have applied to it a coating of a suitable film-forming substance to strengthen, stifien or otherwise modify the properties of the ribbon. Compositions having a basis of cellulose esters, e. g., cellulose nitrate, acetate or aceto-stearate', or cellulose ethers, e. g., ethyl cellulose may be used for this purpose and, especially where the ribbon sections are to be used as strain gauges, the coating may be one which, as described in U. S. Patent No. 2,499,513, leaves unfilled interstices or voids extending through the fabric.

While the resistances can be used as fiat portions of ribbon, in practice, especially with resistances of large ohmic value, it is more convenient to roll or fold the ribbon into a compact unit. Where it is important that the resistance should have a very low inductance, it is preferred to fold the ribbon at the mid point along its length and to roll up the doubled ribbon, as by this means the lowest inductance is ensured. On the other hand a resistance made by rolling the ribbon without first folding it has quite low inductance and offers the advantage that the ends of the resistance, between which in use there may be a substantial potential diilerence, are well separated. In any such rolled up resistance an intermediate layer of insulating material, for example, oiled silk or an insulating film, may

be employed to separate the turns in the roll. The roll may be made on a core or may be wound on. a mandrel subsequently withdrawn to leave mediate layeraof a film of such a substance is used. impregnation of the roll with a solvent for the film-forming substance, e. g., acetone. has the effect of coalescing the yarn and/or film to form a protective coating round the warp and weft, so that. when the solvent has evaporated. a firm, compact package is obtained. Such a solvent can be applied before or continuously with the rolling up of the ribbon; thus, excellent results are given by running the ribbon through a bath of the solvent as it travels to a point where it is rolled up with an intermediate layer of film.

Further protection may be given to such a rolled resistance by coating it with a layer of film-forming substance, nitro-cellulose, ethyl cellulose, or cellulose acetate-stearate being preferable, owing to their high resistance to the effect of moisture. Labels printed with suitable identifying matter, or coloured marking may be applied to the resistance, preferably before such a final coating is applied. Whether or not a copper or other connecting wire woven into the ribbon is provided, it is preferred to provide such rolledup resistances with heavy conductors attached to the ends of the resistance wire or woven-in connecting wire. These heavy conductors may be attached and bent round the ribbon before the latter is rolled; in this way the conductors are securely anchored to the rolled-up resistance.

The accompanying drawings illustrate the construction of resistances in accordance with the invention. In the drawings. which have been drawn to scales chosen merely to show clearly details it is desired to illustrate,

Figures 1 and 2 show two types of resistance in ribbon form;

Figure 3 illustrates diagrammatically apparatus which may be used for forming such ribbons into firm cylinders;

Figure 4 shows a completed cylindrical resistance; and Figures 5 and 6 show out sections of the ribbons shown in Figures 1 and 2 respectively. prepared for use as resistances.

I Referring to Figure 1 of the drawings, the resistance comprises a ribbon generally indicated by reference I woven from a warp yarn 2 of cellulose acetate 'or other insulating material and a weft 3 of wire of high specific resistance lapped with an insulating sheath, e. g. of silk. The ribbon is woven in sections 4 separated by the replacement at intervals of the wire weft 2 by a cotton weftyarn 5. The sections 4 are separated by three pairs of picks of cotton, and between each pair of cotton picks there is a pair of wire picks, the wire being a continuation of that forming the weft in the sections 4. When a section of such a ribbon is to be used as a resistance, of the kind shown in the Figure 5, the ribbon is cut, at each end of the section, between the middle pair of the three pairs of picks of cotton yarn 5. The single pick of cotton yarn adjacent to the cut is then pulled out and cut asaassi 6 offatthepoint2lin1'1sure5.andthepairof wire picks next to it are pulled out and can be used asa connecting lead 22 (Figure 5). If desired the lead 22 can be joined to a heavier wire 23 by means of a soldered joint 24 as shown at the bottom of Figure 5. The remaining pairs of cotton picks 5 at the cut ends hold the adjacent sections 4 from unravelling.

Referrin to Figure 2, the ribbon 6 is likewise divided into sections 4 but by five pairs of picks of cotton yarn 5, and a heavier copper wire I is laid in after the first pair of cotton picks and also before the last pair of cotton picks between each pair of ribbon sections 4. When a section is cut from this type of ribbon to form a resistance, as shown in Figure 6, it is cut between the middle pair of cotton picks 5, the single pick remaining next to the cut is pulled out and cut oil short and the adjacent two picks of resistance wire 3 are pulled out and joined to the adjacent copper wire I at 26. The copper wire I is held securely in the ribbon between two pairs of cotton picks 5. The copper wire I is cut at 21 to avoid an electrical short circuit of the resistance and the end 28 is available for use'as a connecting lead. If the resistance is to comprise more than one section 4 of the ribbon shown in Figure 2, the copper wire 1, other than the lengths at the extreme ends of the resistance which are used as connections, can easily be withdrawn from the fabric;

Referring to Figures 3 and 4. the apparatus shown comprises rotatably mounted shafts I, 9 carrying rolls of the resistance ribbon l and of cellulose acetate film III of similar width respectively. Guide rolls II, I! and i3 determine the path of the ribbon i and guide roll l4 that of the film l0, ribbon I and film Ill being taken up together on a driven take-up roll IS. The bath I6 is charged with a solvent ll for the film l0. e. g., acetone. In operation the ribbon is drawn through the acetone i1 and then rolled up with film III, the acetone plasticising the film so that on drying the roll of ribbon and film form a selfsupporting cylinder which can he slipped from the roller i5, fitted with heavy connecting wires I0 and given a finishing coating with a suitable I film-forming solution to provide a protective layer iii, if desired after the application of identification bands 20.

Having described our invention what we desire to secure by Letters Patent is:

1. An electrical resistance comprising a plurality of elements useful as strain gauges, said elements being in the form of a ribbon woven from a warp of electrically insulating yarn and a weft having a plurality of sections of predetermined length and a pair of connecting leads between each pair of sections, said weft com prising a wire of a uniform diameter of at the most approximately 0.003", said wire forming a plurality of contiguous picks in each section and being continuous throughout the length of said sections and connecting leads, and at least one pair of picks of insulating yarn separating each section from each adjacent connecting lead and at least one further pair of picks of insulating yarn separating adjacent connecting leads from each other.

2. An electrical resistance according to claim 1, wherein each of said sections is followed in succession by two picks of electrically insulating yarn followed by two picks of the wire forming the weft in the sections, two more picks of the yarn,twomorepicksofthewireandthena further two picks of the yarn tollowed by the REFERENCES CITED The following references are of record in the tile 01 this patent:

UNITED s'ra'rns PATENTS Number Name Date 1931204 Schniewindt July 2, 1912 Number Number Name Date Jahr A118. 27, 1912 Craddick et a1 Nov. 21, 1922 Craddick et al. May 22, 1923 Hewitt Feb. 19, 1929 McDill June 19, 1934 Colvin July 3, 1934 Tarpley Sept. 4, 1934 Simmons Aug. 11, 1942 Framburg et al May 9, 1944 Larson May 15, 1945 Jacob Aug. 7, 1945 Levers et a1 Mar. 7, 1950 FOREIGN PATENTS Country Date Great Britain July 20, 1860 Great Britain Sept. 20, 1940 

